You should first learn how to do modeling in Blender, there’s plenty of tutorials on that.
Pick one asset, like a pillar for the chapel, or a bench, or a lamp, but keep it simple.
Learn how to do sub division modeling and create a low and high poly mesh for that asset.
Once that is down, learn how to UV map, bake, and texture that object. For UVing you can do that in Blender. For baking, do it in Blender, or try xNormal or the Handplane3d baker if you want something better and free. You’ll have to use another program to create the texture, at the most basic and free level there is gimp, then there’s a photoshop subscription for $10 a month, or Substance Designer and Painter for $20 a month with the money spent going towards the price of a license. You could also get the Quixel Suite for $100. All decent options. I personally believe photoshop is horrible for texturing for games, since it was never intended to do that.
But anyway, once you have a UV map, even before you texture an asset, you can try putting it in a scene in UE4. I’d suggest using one of the free content example or market place scenes, and just throwing it in and baking the lighting and just playing around with the editor and what you can do with the asset. Once you’re done texturing, you can create a custom material and put it on your asset as well.
From there, make more assets as start working on a scene. You should be able to figure out how to create and get an asset in UE4 in about a week or two. But actually getting good and modeling and texturing, that’s going to take months.